The present invention relates to a wear adjustment device for a brake, particularly a motor vehicle brake, having an adjusting shaft which is mounted in a housing, particularly a caliper, and is accessible from the outside at a front end, which adjusting shaft is equipped with a head part in the accessible area, which head part permits the transmission of a torque.
Brakes having a wear adjustment device of the above-mentioned type are known per se.
Such a wear adjustment device ensures that the lifting play is almost constant for the entire service life, which is achieved by a self-adjustment of the brake linings acting upon a brake disk in the event of a corresponding wear.
If the brake lining is almost completely worn, a new brake lining is installed for avoiding a brake failure. For this purpose, the maintenance mechanic can return the adjusting spindle into its starting position in order to create sufficient space for a new brake lining.
The adjusting spindle can be rotated back only to an end stop, so that there is the risk that a maintenance mechanic may unintentionally try to turn the adjusting spindle although the end stop has been reached. This may result in damage and destruction of the adjustment device.
In order to eliminate this danger, suggestions have been made which basically point into the right direction.
Thus, it is known, for example, from European Patent Document EP 0 566 008 B1 to equip the adjusting shaft with a separating device, particularly also in the form of a desired breaking point, which responds at a certain limit torque. When a permissible limit torque is exceeded, this separating device causes a shearing-off of the outer face-side head area of the adjusting shaft.
Although this reliably prevents an overloading and damaging of the adjustment device and of the brake, the adjusting shaft as a whole is simultaneously also rendered useless.
German Patent Document DE 196 32 917 A1 contains the suggestion to equip the adjusting shaft with a torque-transmitting element which, for preventing the transmission of an undesirably high torque to the shaft, should be deformable.
It is an object of the present invention to design a wear adjustment device of the above-mentioned type such that a limiting of the torque which can be transmitted to the adjusting shaft is permitted without any damage to or destruction of the adjusting shaft itself. In this case, it is simultaneously ensured that the torque which can maximally be transmitted to the adjusting shaft can be determined more precisely.
This object is achieved according to the invention in that, in the case of a wear adjustment device of this type, the head part is constructed as a separate component and, in the axial direction of the adjusting shaft as well as with respect to the adjusting shaft can non-rotatably indirectly or directly be coupled with the latter and is equipped with a desired breaking point which, when a maximally permissible torque is exceeded, results in a shearing-off of the section coupled with the adjusting shaft with respect to the section facing away from the adjusting shaft.
The present invention, on the one hand, avoids the disadvantage of the destruction of or damage to the adjusting shaft in the event of the application of an unacceptably high torque, but also achieves, on the other hand, that the maximally permissible torque leading to the shearing-off can be predetermined within narrow limits, because the shaping of the head part with its desired breaking point can be designed mathematically and also constructively very precisely with respect to the transmissibility of a maximally permissible torque.
In the case of a construction designed for a pure deformation of material, the latter by far cannot be achieved with this precision.
The desired breaking point is formed by a surrounding groove of the head part, which is particularly simple with respect to the construction and manufacturing.
In this case, it is preferable to construct the groove as a notch-type groove with an approximately U-shaped cross-section.
Additional characteristics are the object of additional subclaims.